1. Field of the Invention
The invention relates to a process for the production of perfluoroalkylsulphonyl fluorides by electrochemical fluorination of the corresponding alkylsulphonyl halides and to electrodes for the performance of the process.
2. Description of the Prior Art
The production of fluorinated compounds by electrochemical fluorination proceeds according to E. Hollitzer and P. Satori, Chem.-Ing.-Tech. 58 (1986), no. 1, 31-38 by anodic oxidation in a solvent containing fluoride. Anode materials used in the process are nickel, carbon and platinum. If hydrogen fluoride is used as the solvent, nickel anodes are preferably used. Perfluorinated compounds are obtained from the process.
If alkylsulphonyl halides of the formula C.sub.n H.sub.2n+1 SO.sub.2 X with n=6-10 and X=F, Cl, Br, I are electrochemically fluorinated in hydrogen fluoride on nickel electrodes, perfluoroalkylsulphonyl fluorides, C.sub.n F.sub.2n+1 SO.sub.2 F, are produced. A disadvantage of this process for the production of perfluoroalkylsulphonyl fluorides is considerable anode corrosion. This corrosion gives rise to problems from nickel corrosion products when operating the electrolysis cells, which corrosion products clog the electrode interstices and block valves and pipework. For this reason, prolonged, continuous electrochemical fluorination is not possible, which greatly diminishes the economic viability of the process.
The object of the invention was, therefore, to provide a process for the production of perfluoroalkylsulphonyl fluorides by electrochemical fluorination in which the stated disadvantages do not arise.
It was surprisingly found that the stated disadvantages do not arise if the anodes consist of nickel with a columnar structure or are coated with nickel with such a structure.